1. Field of the Invention
The present invention relates to an orthogonal frequency division multiplexing (OFDM) receiver using an a plurality of antennas mounted on a movable object, particularly a technology to reduce an interference between carriers due to Doppler shift associated with movement of the movable object.
2. Description of the Related Art
In ground digital broadcasting, OFDM is adopted. When an OFDM signal is received in a movable object such as a car, inter-carrier interferences (ICI) due to Doppler shift occurred by a high-speed movement of the movable object must be considered.
Receivers mounted on the movable object and receiving an OFDM signal have been proposed. In a receiver proposed by, for example, Japanese Patent Laid-Open No. 9-284251, the OFDM signal is received by a plurality of antennas arranged so as to provide directivities in different directions, signals of a desired channel are extracted from received signals output the antennas, respectively, and sent to automatic frequency control (AFC) circuits, respectively. The AFC circuits remove frequency errors of the received signals due to Doppler shift. The received signals from which the frequency errors are removed are combined with a combining unit. The output signal of the combining unit is sent to the demodulator/decoder and OFDM-demodulated and decoded. As a result, influence of the inter-carrier interferences due to Doppler shift is removed. Therefore, it is possible to reproduce information of a video and a speech.
Generally, a large scale circuit is necessary for detecting frequency errors due to Doppler shift. It is thought that the above proposed technology detects frequency errors due to Doppler shift from the received signals from the antennas, independently. Accordingly, a circuit scale increases with an increase of the number of antennas. This contributes to large-sizing of the receiver and increase of power consumption.
It is an object of the present invention to provide an OFDM receiver for a movable object, which makes it possible to decrease a circuit scale to be necessary for an estimation of Doppler frequency without depending on increase of the number of antennas.